Programmable photolithographic mask system and method

ABSTRACT

The present invention overcomes many of the disadvantages of prior lithographic microfabrication processes while providing further improvements that can significantly enhance the ability to make more complicated semiconductor chips at lower cost. A new type of programmable structure for exposing a wafer allows the lithographic pattern to be changed under electronic control. This provides great flexibility, increasing the throughput and decreasing the cost of chip manufacture and providing numerous other advantages. The programmable structure consists of an array of shutters that can be programmed to either transmit light to the wafer (referred to as its “open” state) or not transmit light to the wafer (referred to as its “closed” state). The programmable structure can comprise or include an array of selective amplifiers. Thus, each selective amplifier is programmed to either amplify light (somewhat analogous to the “open” or “transparent” state of a shutter) or be “non-amplifying” (its “closed” or “opaque” state). In the non-amplifying state, some portion of the incident light is transmitted through the amplifier material. The shutters and selective amplifiers can work in tandem to form a “programmable layer”. A programmable technique is provided for creating a pattern to be imaged onto a wafer that can be implemented as a viable production technique. Thus, the present invention also provides a technique of making integrated circuits. A diffraction limiter can be used to provide certain advantages associated with contact lithography without requiring some of the disadvantages of contact lithography.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/051,121 filed Jun. 27, 1997 entitled “A Shutter For aProgrammable Photon Lithography Mask”; U.S. Provisional Application No.60/058,701 filed Sep. 12, 1997 entitled “A Doped Solid-State LithographyMask”; U.S. Provisional Application No. 60/058,702 filed Sep. 12, 1997entitled “A Device to Improve Resolution In Lithography Using AProgrammable Mask”; and U.S. Provisional Application No. 60/060,254filed Sep. 29, 1997 entitled “A Selective Amplifier For a ProgrammablePhoton Lithography Mask.”

FIELD OF INVENTION

[0002] This invention relates to microfabrication, and more particularlyto systems, methods, and techniques for manufacturing integrated circuitchips using photon lithography. Still more particularly, the presentinvention relates to systems, methods, and techniques in connection withprogrammable masks for microlithography.

BACKGROUND AND SUMMARY OF THE INVENTION

[0003] Lithography is used to transfer a specific pattern onto asurface. Lithography can be used to transfer a variety of patternsincluding, for example, painting, printing, and the like. More recently,lithographic techniques have become widespread for use in“microfabrication”—a major example of which is the manufacture ofintegrated circuits such as computer chips.

[0004] In a typical microfabrication operation, lithography is used todefine patterns for miniature electrical circuits. The lithographydefines a pattern specifying the location of metal, insulators, dopedregions, and other features of a circuit printed on a silicon wafer orother substrate. The resulting semiconductor circuit can perform any ofa number of different functions.

[0005] Improvements in lithography have been mainly responsible for theexplosive growth of computers in particular and the semiconductorindustry in general. The major improvements in lithography can, for themost part, be put into two categories: an increase in chip size, and adecrease in the minimum feature size (improvement in resolution). Bothof these improvements allow an increase in the number of transistors ona single chip (and in the speed at which these transistors can operate).For example, the computer circuitry that would have filled an entireroom in 1960's technology can now be placed on a silicon “die” the sizeof your thumbnail. A device the size of a wristwatch can contain morecomputing power than the largest computers of several decades ago.

[0006] One type of lithography that is commonly used in the massproduction of computer chips is known as “parallel lithography”.Parallel lithography generally prints an entire pattern at one time.This is usually accomplished by projecting photons through a mask onto aphotoresist-coated semiconductor wafer, as shown in FIG. 1. A mask(designated by an “M” in FIG. 1) provides a template of the desiredcircuit. A photoresist coat, which may be a thin layer of materialcoated on the wafer which changes its chemical properties when impingedupon by light, is used to translate or transfer the mask template ontothe semiconductor wafer. In more detail, mask M allows photons (incidentlight, designated by an “I” ) to pass through the areas defining thefeatures but not through other areas. An example of a typical maskconstruction would be deposits of metal on a glass substrate. In a wayanalogous to the way light coming through a photographic negativeexposes photographic paper, light coming through the mask exposes thephotoresist. The exposed photoresist bearing the pattern selectively“resists” a further process (e.g., etching with acid, bombardment withvarious particles, deposition of a metallic or other layer, etc.) Thus,this lithography technique using photoresist can be used to effectivelytranslate the pattern defined by the mask into a structural pattern onthe semiconductor wafer. By repeating this technique several times onthe same wafer using different masks, it is possible to buildmulti-layered semiconductor structures (e.g., transistors) andassociated interconnecting electrical circuits.

[0007] Parallel lithography as described above has the advantage that itis possible to achieve a high throughput since the whole image is formedat once. This makes parallel lithography useful for mass production.However, parallel lithography has the disadvantage that a new mask isrequired each time one desires to change patterns. Because masks canhave very complex patterns, masks are quite costly and susceptible todamage.

[0008] For mass production, parallel lithography is usually done using amachine known as a “stepper.” As schematically depicted in FIG. 1, astepper consists of a light source (“I”), a place to hold a mask (“M”),an optical system (“lenses”, “L”) for projecting and demagnifying theimage of the mask onto a photoresist-coated wafer (“W”), and a stage(“S”) to move the wafer. The process of exposing a wafer using a stepperis summarized in FIG. 2A, and is depicted from a side view in FIGS.2B-2E. In each exposure, a stepper only exposes a small part of thewafer, generally the size of one chip. Since there are often manyseparate chips on each wafer, the wafer must be exposed many times. Thestepper exposes the first chip (FIG. 2B), then moves (“steps”) over(FIG. 2C) to expose the next chip (FIG. 2D) and repeats this process(FIG. 2E) until the entire wafer is exposed. This process is known as“step and repeat” and is the origin of the name “stepper.”

[0009] A stepper must also be capable of precisely positioning the waferrelative to the mask. This precise positioning (overlay accuracy) isneeded because each lithography step must line up with the previouslayer of lithography. A stepper spends a significant portion of its timepositioning the stage and the rest exposing the photoresist. Despite thegreat precision necessary, steppers must be capable of high throughputto be useful for mass production. There are steppers that can processone hundred 8-inch wafers per hour.

[0010] One way to increase the usefulness of a chip is to increase itssize. In the “step and repeat” example described above, the size of thechip is limited to the exposure size of the stepper. The exposure sizeis small (roughly 20 mm×40 mm) because of the cost of an optical systemthat is capable of projecting a high quality image of the mask onto thewafer. It is very expensive to increase the size of a chip by increasingthe exposure size of the stepper (for example, this would require alarger lens—which by itself can cost many hundreds of thousands ofdollars). Another approach is to modify a stepper so that light onlyshines on a subsection of the mask at a given time. Then, the mask andwafer can be scanned (moved relative to the fixed light source)simultaneously until the entire mask is imaged onto the wafer, as inFIGS. 3A-3C. This modified stepper is known as a “scanner” or“scanner/stepper”.

[0011] Scanners offer increased chip size at the expense of increasedcomplexity and mask costs. Because scanner masks are larger, the masksare more fragile and are more likely to contain a defect. The increasedsize and fragility of the mask mean that the masks for a scanner will bemore expensive than the masks for a stepper. Also, because the image isbeing demagnified, the mask and wafer must be scanned at differentspeeds, as depicted by the length of the arrows in FIGS. 3A-3C. Becauseof the great precision required, differential scanning increases thecost and complexity of a scanner when compared with a stepper.

[0012] Many chip manufacturers are looking toward future improvements inresolution and/or exposure size to help continue the growth that hasdriven the semiconductor industry for the past thirty years. Theimprovements in these areas have been partly the result of improvementsin the optical systems used to demagnify the mask and of the use ofshorter wavelength light. In particular, modem lithography systems usedfor mass production are “diffraction limited”, meaning that the smallestfeature size that it is possible to print is determined by thediffraction of light and not by the size of features on to the mask. Inorder to improve the resolution, one must use either a shorterwavelength of light or another technique such as optical proximitycorrection or phase shifting.

[0013] Another option for improving resolution is to put the mask incontact with the wafer, as in FIG. 4; the effects of diffraction can belessened by not giving the light a chance to “spread out” after itpasses through the mask. Unfortunately, contact lithography is notsuitable for mass production for at least two reasons. First, the maskmust now be the same size as the final pattern, making the mask moreexpensive and more fragile. Second, because the mask is in contact withthe wafer, it is easily damaged.

[0014] The present invention overcomes many of the disadvantages ofprior lithographic microfabrication processes while providing furtherimprovements that can significantly enhance the ability to make morecomplicated semiconductor chips at lower cost.

[0015] One aspect provided by this invention provides a new type ofprogrammable structure for exposing a wafer. The programmable structureallows the lithographic pattern to be changed under electronic control.This provides great flexibility, increasing the throughput anddecreasing the cost of chip manufacture and providing numerous otheradvantages.

[0016] The programmable structure provided in accordance with oneexample embodiment of the invention consists of an array of shuttersthat can be programmed to either transmit light to the wafer (referredto as its “open” state) or not transmit light to the wafer (referred toas its “closed” state). A simplified example lithography systemincorporating such a programmable mask is schematically depicted in FIG.5A exposing an example pattern. In FIG. 5B the same programmable maskPPM is shown exposing a different pattern.

[0017] The programmable mask shown in FIGS. 5A and 5B can provide atwo-dimensional array of individual shutters each of which can beprogrammed to either transmit light (“open”, “transparent”) or blocklight (“closed”, “opaque”). At least one such two-dimensional array ofstructures can be placed between a wafer and a source of electromagneticenergy. Each of the structures may comprise an active region supportingan electron distribution that can be changed to affect the modulation ofelectromagnetic energy from said source. The structures can becontrolled to selectively modulate, in accordance with a programmablepattern, electromagnetic energy impinging on the wafer.

[0018] In accordance with this aspect provided by the invention, asystem for exposing a wafer may comprise a source of electromagneticenergy, a collimating lens optically coupled to the electromagneticenergy source, a wafer stage, and a two-dimensional array of structuresdisposed between the wafer stage and the collimating lens. Each of thestructures in the array may comprise an active region supporting anelectron distribution that can be changed to affect the modulation ofelectromagnetic energy from said source. An electrical controllercoupled to the two-dimensional array may be used to electrically controlthe semiconductor structures to selectively modulate, in accordance witha changeable pattern, electromagnetic energy from the source that isdirected toward the wafer stage.

[0019] In accordance with a further aspect provided by the presentinvention, the programmable structure can comprise or include an arrayof selective amplifiers. In accordance with this aspect provided by theinvention, a programmable electromagnetic energy modulating structurecomprises a two-dimensional array of solid-state selective amplifierseach comprising regions of permanently opaque material and activeregions. Control circuitry disposed within the array can be provided toselectively control each of the active regions to toggle between anamplifying state and a non-amplifying state. Thus, each selectiveamplifier is programmed to either amplify light (somewhat analogous tothe “open” or “transparent” state of a shutter) or be “non-amplifying”(its “closed” or “opaque” state). In the non-amplifying state, someportion of the incident light is transmitted through the amplifiermaterial. The portion of incident light that is transmitted through theamplifier can range from 0-100%, depending on the specific design andoperating conditions. Selective amplification has all of the advantagesof a programmable structure that uses shutters with several addedadvantages—including reduction in the time required to expose theresist.

[0020] In accordance with a further aspect provided by the invention theshutters and selective amplifiers can work in tandem to form a“programmable layer”. When the programmed pattern calls for light topass (or, not pass) through a particular pixel, both the selectiveamplifier and shutter corresponding to that pixel would be put intotheir open (or, closed) state. FIGS. 6A-6F schematically depicts theoperation of an example shutter (labeled as “SIT”) (FIGS. 6A-6B), anexample selective amplifier (labeled as “AM”) (FIGS. 6C-6D), and anexample device (labeled as “X”) combining the two (FIGS. 6E-6F). In eachof is these figures, “I′” represents the intensity of light incident onthe shutter/amplifier, and “I′” represents the light intensity afterinteracting with the shutter/amplifier. Combining a selective amplifierwith a shutter in this manner achieves increased contrast over selectiveamplification alone.

[0021] In accordance with another aspect provided by the presentinvention, a programmable technique is provided for creating a patternto be imaged onto a wafer that can be implemented as a viable productiontechnique. Thus, the present invention also provides a technique ofmaking integrated circuits. In accordance with this aspect provided bythe invention, a wafer having a surface covered with photoresist isplaced on a movable wafer stage. A source directs electromagnetic energytoward a two-dimensional array of semiconductor structures disposedbetween the source and the wafer stage. The electron distribution withinthe structures is electrically controlled to define a desiredmicrofabrication exposure pattern that modulates electromagnetic energyfrom said source that impinges on the wafer in accordance with apattern. The modulated energy is used to expose the photoresist with thepattern. The wafer is then etched to selectively remove portions of thephotoresist based on the desired microfabrication exposure pattern, andthe etched wafer is treated to construct a semiconductor structure layeron the wafer.

[0022] In accordance with a further aspect provided by this invention, adiffraction limiter can be used to provide certain advantages associatedwith contact lithography without requiring some of the disadvantages ofcontact lithography. In accordance with this aspect of the invention,the diffraction limiter may provide an opaque layer in which there is anarray of transparent regions (“holes”) distributed in a one-to-onecorrespondence to the selective amplifiers/shutters. The diffractionlimiter is placed in contact with the wafer, and the light that passesthrough the programmable layer is incident upon it. The diffractionlimiter allows the advantages of contact lithography while maintainingthe distance between the programmable layer and wafer.

[0023] In accordance with a further aspect provided by the presentinvention, a programmable shutter array, a programmable selectiveamplifier array, and a diffraction limiter can all be used in a commonsystem. For example, FIG. 7A depicts schematically a lithography setupincorporating the above three components. FIG. 7B shows a zoomed-in viewof the diffraction limiter (denoted by “D”) and wafer section. Thesethree components provide a programmable lithography system that offershigh throughput, extremely accurate pattern reproduction, and excellentresolution.

[0024] Implementing a diffraction limiter in conjunction with anyprogrammable lithography system should significantly reduce thedisadvantages associated with contact lithography. This device is placedin contact with the wafer and thus reduces the effects of diffraction(see FIGS. 7A and 7B.) Even though the diffraction limiter is close tothe wafer and could be damaged, it is inexpensive and is easilyreplaced. Additionally, one can apply techniques such as phase shiftingand/or optical proximity correction on the diffraction limiter itselfBecause of the simple, regular shape of the pixels on the diffractionlimiter, such corrections should be easily optimized.

[0025] Lithography in accordance with the present invention potentiallyallows a high throughput to be achieved. For example, only a singleprogrammable structure is necessary to print any desired pattern. Anon-exhaustive list of some of the many features and advantages providedby the present invention are as follows:

[0026] Programmable lithography offers increased flexibility overconventional parallel lithography. This increased flexibility means thata greater variety of chips can be easily produced. It also opens up waysto improve the manufacture of all types of semiconductor products. Italso simplifies the entire process of designing and manufacturingsemiconductor products.

[0027] No need to have different masks to produce different chips.Because a single programmable structure can be programmed with anarbitrary pattern, it is no longer necessary to fabricate (and purchase)new mask sets in order to print new chips. This is extremelycost-effective for producing small quantities of specialized chipsbecause the cost of a mask set can be prohibitively expensive. Inproducing large quantities of chips the cost of the mask set is lesssignificant because it is a fixed cost amortized over many more chips.

[0028] Electronic alignment. Because it is extremely important to lineup the current lithography step with previous steps, steppers spend asignificant amount of time mechanically aligning the wafer with themask. With programmable lithography the pattern can be programmed intothe “programmable layer” (i.e. the programmable area within the mask)such that it is aligned with the wafer. This saves time over having tomechanically align as in the case of a conventional mask.

[0029] Disconnecting the size of the chip from the exposure size of thestepper. In conventional parallel lithography, the size of a chip isdetermined by the exposure size of the stepper. However, withprogrammable lithography a different pattern can be loaded into theprogrammable layer at each exposure. Hence, there is no longer anyreason that the same pattern needs to be imaged each time the stepperdoes an exposure. Consequently, in programmable lithography, the size ofthe chip is not intrinsically determined by the size of each individualexposure. This “disconnect” between chip and exposure size is asignificant advantage of programmable lithography because chipperformance and chip size are closely tied together.

[0030] Simplified optical proximity correction. Optical proximitycorrection is a technique that is used to increase the resolution of theoptical system at a given wavelength of light. Because of diffraction,the pattern on the mask is not faithfully reproduced on the wafer. Inorder to compensate for this, the pattern on the mask can be altered toaccount for diffraction so that the desired pattern can be imaged ontothe wafer. One problem with this technique in a conventional mask isthat it is difficult to decide how to alter the shape on the mask suchthat the desired shape will appear on the wafer. This is mainly due tothe size and complexity of the desired pattern. Programmable lithographygreatly simplifies this problem because in programmable lithography thesame shape (e.g., a square) is always being imaged onto the wafer byeach pixel, and the correction can be made on a pixel-by-pixel basis.

[0031] Simplified phase shifting. As with optical proximity correction,phase shifting is also a technique that is used to increase theresolution of the optical system at a given wavelength of light. In thistechnique, a material that causes a phase shift in light is placed onthe mask. The phase shifting material causes destructive interference atthe wafer between light from neighboring features in order to eliminatethe diffraction tails. Phase shifting also suffers from the same problemas optical proximity correction; due to the size and complexity of thepattern it is difficult to decide where to place the phase shiftingmaterial. As with optical proximity correction, programmable lithographyallows this problem to be greatly simplified because the same shape isalways being imaged onto the wafer at each pixel. Programmablelithography also allows the possibility of active phase shifting. Inactive phase shifting, each pixel would contain an additional layer inwhich there would be a material whose index of refraction changes when avoltage is applied.

[0032] Simplification of the chip making process. One of the bigproblems facing chip manufacturers is the growing complexity of the chipmaking process. With each new chip the manufacturer must get a brand newmask set. They must also inspect and repair these masks. Withprogrammable lithography only a single programmable structure is neededto produce an entire chip. In the event that a programmable mask breaksit can simply be replaced with another identical programmable mask.Additionally, programmable lithography will facilitate research anddevelopment of new products because of the greater ease of producingprototype devices.

[0033] The shutters and/or selective amplifiers can be fabricatedeasily. Each individual shutter can be a device similar to devices thatare typically used in chips themselves. This allows the design andfabrication of the shutter to draw on the enormous amount of knowledgeassociated with production techniques and operation of these devices.

[0034] The shutters and/or selective amplifiers can be small and denselypacked. Small shutters mean that the lithography system can producesmall features without the need for demagnification, although it couldbe used in a system that does include demagnification. Densely packedshutters mean high throughput because they reduce the number ofexposures necessary to expose the entire wafer.

[0035] The shutters and/or selective amplifiers can work for shortwavelength light. Shorter wavelengths provide better resolution, whichis important for chip performance.

[0036] The shutters and/or selective amplifiers generally will not breakduring normal operation. This is important because the mask must be ableto flawlessly reproduce the desired image. If even a single pixel isincorrect then the entire chip is likely to be worthless.

[0037] The shutters and/or selective amplifiers can switch statesquickly. The speed of the shutters is relevant for throughput and maybecome significant when many shutters must be addressed.

[0038] Selective amplifiers can be used alone and/or in combination withprogrammable shutters. An array of selective amplifiers can be used inthe place of or in addition to a PPM to project more light onto thewafer in some areas than in others corresponding to the pattern to beimaged. Or, an array of selective amplifiers can be used in astand-alone system, e.g., when the non-amplified light is not sufficientto expose the resist and the amplified light is.

[0039] Programmable lithography provides a resolution and throughputcomparable to conventional parallel lithography while retaining all ofthe advantages of programmable lithography.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] These and other features and advantages provided by the presentinvention will be better and more completely understood by referring tothe following detailed description of presently preferred exampleembodiments in conjunction with the drawings, of which:

[0041]FIG. 1 shows an example prior art technique of parallellithography using a stepper;

[0042]FIG. 2A summarizes the operation of an example prior art stepper;

[0043]FIGS. 2B to 2E show the simplified operation of an example priorart stepper;

[0044]FIGS. 3A to 3C show the simplified operation of an example priorart scanner;

[0045]FIG. 4 shows an example prior art contact lithography technique;

[0046]FIGS. 5A and 5B show a simplified example of technique oflithography in accordance with a preferred embodiment of the presentinvention using a programmable structure;

[0047]FIGS. 6A and 6B illustrate example operation of shutters providedin accordance with the present invention;

[0048]FIGS. 6C and 6D illustrate example operation of selectiveamplifiers provided in accordance with the present invention;

[0049]FIGS. 6E and 6F illustrate example operation of a combinationshutter/selective amplifier array in accordance with the presentinvention;

[0050]FIG. 7A shows an example lithography setup in accordance with apresently preferred example embodiment of the present invention;

[0051]FIG. 7B shows a zoomed-in view of the diffraction limiter andwafer of FIG. 7A;

[0052]FIG. 8 shows a more detailed example embodiment of the inventionand its components in accordance with the present invention;

[0053]FIG. 9 shows an example single selective amplifier and itscomponents in accordance with the present invention;

[0054]FIG. 10 shows an example single shutter and its components inaccordance with the present invention;

[0055]FIG. 11 shows an example single programmable pixel and itscomponents in accordance with the present invention;

[0056]FIGS. 12A to 12H show an example technique of programmablelithography for a “4-step programmable layer” in accordance with thepresent invention;

[0057]FIG. 13A summarizes an example electronic alignment technique inaccordance with the present invention;

[0058]FIGS. 13B to 13G shows an example electronic alignment techniquein accordance with the present invention; and

[0059]FIGS. 14A to 14F show an example technique in accordance with thepresent invention for printing chips that are larger than the exposuresize of the mask.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0060] In an example preferred embodiment, the invention consists ofthree main components: an array of selective amplifiers 10, an array ofsolid-state shutters 12, and a diffraction limiter 14. Taken together,the array of amplifiers 10 and the array of shutters 12 form what weshall call a “programmable layer”, PL. FIG. 8 shows these threecomponents incorporated into an example setup for performinglithography. In this figure, incident light, I, shines on theprogrammable layer from above. A pattern generator feeds theuser-defined pattern into the programmable layer.

[0061] The array of selective amplifiers 10 consists of regions of apermanently opaque material 22 (a metal such as aluminum) and activeregions 20. Each active region 20 within the array of selectiveamplifiers 10 is associated with a single selective amplifier 40. Theactive regions 20 can be toggled between a non-amplifying 20 a andamplifying 20 b state via control circuitry (designated by an encircledC1).

[0062] Following the array of selective amplifiers 10 is an array ofsolid-state shutters 12. The array of solid-state shutters 12 consistsof regions of a permanently opaque material 22 and active regions 24.Each active region 24 within the array of shutters 12 is associated witha single shutter 60. The active regions 24 can be toggled between anopaque 24 a and a transparent 24 b state via control circuitry(designated by an encircled C2).

[0063] For reference, a given selective amplifier 40 and itscorresponding solid-state shutter 60 will be taken as a “programmablepixel” 100.

[0064] A diffraction limiter 14 is placed in contact with aresist-coated wafer. The diffraction limiter 14 is comprised of regionsof a transparent material 30 (such as single crystal sapphire) andregions of an opaque material 32 (a metal such as aluminum). In thepreferred embodiment, this is accomplished by depositing opaque materialsuch as aluminum onto a transparent substrate such as sapphire. Thetransparent regions individually correspond to the locations of theactive regions of the programmable pixels in the programmable layer.

[0065]FIG. 9 details a single selective amplifier 40. Each singleselective amplifier 40 consists of a section (46, 48, 50, 52) capable ofselectively amplifying a beam of light, the circuitry C1 needed tocontrol the state of the selective amplifier, and a material 22 thatblocks the light between adjacent selective amplifiers. In the preferredembodiment, the section capable of selectively amplifying light is ajunction 52 between a p-type semiconductor 48 (such as p-doped GaN) andan n-type semiconductor 50 (such as n-doped GaN) with metal contacts 46(such as aluminum) that are used to bias the junction 52. The controlcircuitry C1 would be capable of turning the bias on or off. The planeof the p-n junction 52 is oriented such that the normal of the plane isperpendicular to the incoming light. The p-n junction 52 is exposed tothe incident light through a hole 44 in the permanently opaque region22. The semiconductor materials 48 and 50 must be chosen such thatstimulated emission occurs for the wavelength of incident light beingused.

[0066]FIG. 10 details a single solid-state shutter 60. Each singlesolid-state shutter 60 consists of a section (66, 68, 70, 72) capable ofeither blocking or transmitting the incident light, the circuitry C2needed to control the state of the shutter, and a material 22 thatblocks the light between adjacent shutters. In the preferred embodiment,the section capable of either blocking or transmitting light is a MOSstructure: an insulator region 68 (such as SiO₂) is sandwiched betweenmetal electrodes 66 (such as aluminum) and a semiconductor region 70(such as n-doped (n++) GaN). Control circuitry C2 is used to bias theMOS structure across the electrodes 66. The active region 72 is exposedto the incident light through a hole 64 in the permanently opaque region22.

[0067]FIG. 11 details a programmable pixel 100. Each programmable pixel100 consists of a single selective amplifier 40, a single shutter 60, atransparent insulator 102 (such as SiO₂) between the amplifier andshutter, the control circuitry, represented by an encircled C1 and C2,needed to control the state of the pixel, and a material 22 that blocksthe light between adjacent pixels. The active region of the amplifierportion 52 must overlap the active region of the shutter 72 to form theactive region of the pixel 104. The active region of the pixel 104 isexposed to the incident light through a hole 106 in the permanentlyopaque region 22.

[0068] The combined control circuitry, C1 and C2, needs to be capable oftoggling a voltage across each individual pixel 100 depending on thepattern supplied by the user via the pattern generator. This controlcircuitry is similar to the standard type of addressing used in memorydevices or an LCD.

[0069] The above-described example embodiment is specified as to beuseful in a lithography system utilizing (approximately) 385 nm (andlonger) wavelength light. However, there are many other possibleembodiments. For instance, the choice of specific materials for thevarious semiconductors and insulators can render the system useful forother wavelengths of incident light. Specifically, the band gap of thesemiconductor in the selective amplifier determines the wavelengths oflight that can be amplified. Of course, the materials chosen for theamplifier must be capable of amplifying light. For example, this couldbe accomplished in the manner described in the ensuing theory ofoperation section. Likewise, for the shutter, the materials used can beoptimized for operation with a selected wavelength of incident light,again described in the theory of operation section.

[0070] Also, the specific geometry of electrodes and active materialscould be modified while still retaining the usefulness of the invention.For instance, all the electrodes could be placed on the top surface ofthe device. Or, for example, the orientation of the plane of thejunctions does not necessarily need to be completely perpendicular tothe incoming light. This could simplify the fabrication process of thepixels.

[0071] Furthermore, since shorter wavelengths are desirable inlithography, materials with a large band gap are desirable for use inthe pixels. In fact, some materials that may not typically be thought ofas semiconductors may be useful for our purposes because they have alarge band gap, such as sapphire, diamond, SiO₂, LiF, ZnS, AlN, ZnSe,etc. . . Additionally, in the amplifier section, our invention useselectric fields to induce a population inversion, but this is not theonly possible means of doing so. Other techniques include but are notlimited to optical pumping, thermal pumping, etc. . . Similarly, in theshutter section, our invention uses electric fields to change thedensity of occupied states, but this is not the only possible means fordoing so. Other techniques include but are not limited to changing thetemperature of the semiconductor or shining light onto thesemiconductor.

[0072] There is a large field of research devoted to controllingpopulation densities for the purpose of creating, manipulating,blocking, or amplifying light. One active area of interest in this fieldis the creation of semiconductor lasers. Many of the structures createdfor semiconductor lasers or optical amplifiers could be used forselective amplification (in fact, semiconductor lasers could be used inthe place of the selective amplifiers, in which case an external lightsource would not be necessary.) These other structures would include butwould not be limited to heterostructures and vertical cavity surfaceemitting lasers (VCSELs). Similar structures could also be used for theshutter. While these other structures operate on similar principles tothose described in the theory of operation section, they might providesome advantages, like decreasing the amount of voltage or currentrequired to operate the device, or increasing the area of the activeregion.

[0073] There are also many possible alternate embodiments for thediffraction limiter. The materials must merely satisfy the requirementthat the transparent regions individually correspond to the locations ofthe active regions of the programmable pixels in the programmable layerwith opaque regions in between. For instance, the transparent regionscould be physical holes etched through an opaque substrate, or, thetransparent and opaque regions could be semiconductors with varyinglevels and/or kinds of doping.

[0074] Example Operation of Preferred Embodiments

[0075] In accordance with the preferred embodiments described above,each individual pixel 100 has the ability to either block or amplifylight, I, and is able to be toggled between the two settings by means ofthe control circuitry C1 and C2. The pattern generator will control theindividual pixels 100 in such a way that the control circuitry C1 and C2always act in tandem within a given pixel.

[0076] The pattern generator addresses the control circuitry C1 tocontrol a potential difference across the metal contacts 46. If thesemiconductor 48 is doped n-type and the semiconductor 50 is dopedp-type, then a depletion region is created in the active region 52. Whena potential difference is applied across the contacts 46, a populationinversion is formed in the depletion (active) region 52. Incident lightof the appropriate wavelength causes stimulated emission and is thusamplified in the active region 52. If no potential difference is appliedacross the contacts 46, the light passes through the region 52unaltered. This satisfies our requirement for a selective amplifier.

[0077] The pattern generator simultaneously addresses the controlcircuitry C2 to control a potential difference across the metal contacts66. When a potential difference is applied, this changes both thedensity of states and the conductivity of the semiconductor 70 in theregion 72 adjacent to the semiconductor-insulator (70-68) interface. Forinstance, if the semiconductor 70 is doped n-type and a proper potentialdifference is applied across the metal contacts 66, then a depletionregion is created in the active region 72. In the depletion (active)region 72 the conduction band electrons are repelled by the electricfield created by the bias. The conductivity is dramatically decreased inthe depletion (active) region 72. The density of occupied states in thedepletion (active) region 72 is also changed because the states at thebottom of the conduction band that were previously filled are no longerfilled. Hence, incident light with energy less than the semiconductor 70band gap is transmitted through the device in the presence of apotential difference, and is absorbed in the absence of a potentialdifference. (Conversely, as per the theory of operation section, certainwavelengths of light with an energy greater (including x-rays) than thesemiconductor 70 band gap are transmitted through the device in theabsence of a potential difference, and are absorbed in the presence of apotential difference.) This satisfies our requirement for a shutter.

[0078] In order to utilize the programmable layer, PL, one must do aseries of exposures of the photoresist 33. Between each exposure twoactions can be taken: (a) any or all of the pixels 100 can be toggled toa new state, and/or (b) the substrate can be moved, if necessary. Byselecting which pixels 100 to make opaque or transparent themanufacturer can generate any pattern that he or she desires. FIGS. 12Ato 12H depict an example of this process using what we shall call a“4-step programmable layer.” The term “4-step” means that in order tocreate a pattern that fills the entire area of the mask, the substratemust be exposed four times. Each step is shown in a different pair offigures, one representing a perspective view and the other representinga top view. For example, FIGS. 12A and 12B both depict the firstexposure step, from differing views. In the example depicted, theprinting of the desired pattern is completed in the last step, shown inFIGS. 12G and 12H. Another case would be if the programmable layer weredesigned such that the desired pattern could be printed without needingto move the substrate at all (similar to the setup in FIG. 7A).Lithography using this “1-step programmable layer” would act as a fullyparallel process.

[0079] A light source, I, illuminates the programmable layer, PL, fromabove and the light transmitted 31 by the layer passes through a lens,L, and is demagnified. After demagnification, the image of theprogrammable layer, PL, impinges on the diffraction limiter 14 which isheld in close proximity with a substrate coated with a photosensitiveresist 33 as in FIG. 8. Light 31 is only transmitted through thediffraction limiter in transparent regions 30 and not through regionscovered by opaque material 32, and thus exposes the resist in regions35. The same setup is depicted in a more schematic way in FIG. 7A forpurposes of clarity.

[0080] One example technique for electronic alignment is summarized inFIG. 13A. FIG. 13B shows a wafer, W, that has been previously processed.FIG. 13C shows the pattern that the user intends to add and its positionrelative to the previously processed features. FIG. 13D shows theprogrammable layer, PL, coarsely aligned with the wafer. At this stage,the programmable layer is not yet aligned to with a pixel, and if anexposure were made the resulting pattern would be misaligned with thepreviously processed features as in FIG. 13E. FIG. 13F shows theprogrammable layer after alignment to within a pixel, and the subsequentsuccessful exposure. Given a different coarse alignment, FIG. 13G showsthe case in which a different individual pixel in the programmable layerhas been aligned with the previously processed features, and thesubsequent successful exposure. FIGS. 13F-13G together demonstrate thatthe absolute location of the programmable layer relative to the wafer isnot important as long as the programmable layer is aligned to within anysingle pixel. The pattern can be electronically shifted to a new set ofpixels in the programmable layer such that they will project the imagein the correct location.

[0081] An example of how to use an example preferred embodiment providedin accordance with the present invention to disconnect the chip sizefrom the exposure size is summarized in FIG. 14A. FIG. 14B shows thepattern that the user intends to print on the wafer, W. Note that thispattern is about four times the single exposure size of the programmablelayer, PL. In each of the FIGS. 14C-14F, the programmable layer isloaded with the proper section of the total pattern, an exposure ismade, and the wafer is moved to the left by a fixed amount. In FIG. 14F,the desired pattern has been printed.

[0082] Theory of Operation

[0083] We begin with a discussion of an example shutter in accordancewith the present invention, followed by a discussion of an exampleselective amplifier in accordance with the present invention.

[0084] For the preferred embodiment array of shutters to work, it isnecessary that the various shutters can be made either “transparent” or“opaque” to the incident light. For a mask, both terms “transparent” and“opaque” describe the ratio of the intensity of incident light to theintensity of transmitted light. An “opaque” material is differentrelative to a “transparent” material in that the amount of lightattenuated is much greater in the case of the “opaque” material. Theamount of attenuation is best measured using the concept of anattenuation coefficient, α, defined by the relation $\begin{matrix}{{\frac{I}{I_{o}} = e^{{- \alpha}\quad z}},} & (1.)\end{matrix}$

[0085] where I is the transmitted intensity, I₀ is the incidentintensity, and z is the thickness of material traversed. Using this, ifwe compare the transmitted intensities through a “transparent” materialand an “opaque” material, we get a measure of the contrast in lightimpinging on the resist, C, as $\begin{matrix}{C = {\frac{I_{transparent}}{I_{opaque}} = {\frac{e^{{- \alpha_{transparent}} \cdot z}}{e^{{- \alpha_{opaque}} \cdot z}} = {e^{{+ {({\alpha_{opaque} - \alpha_{transparent}})}} \cdot z}.}}}} & (2.)\end{matrix}$

[0086] If this contrast is a large number, the resist will only beactively is exposed when the shutter is in the “transparent” state.Thus, if we can control the attenuation coefficient in a material, i.e.vary it from α_(transparent) to α_(opaque) so that their difference isappreciable, then the system is a useful candidate for a programmablemask.

[0087] The attenuation coefficient, α, arises from all possiblemechanisms of absorption of the light combined. For our system, the twomechanisms we are most interested in are (a) absorption by “free”carriers in the conduction band, and (b) atomic/interband photoeffect.

[0088] Absorption by “free” Carriers in the Conduction Band

[0089] In a simple classical model of conduction, the conductivity of amaterial is directly proportional to the number of free electrons perunit volume available to interact. These charges are capable ofabsorbing or reflecting the incident light. If the fields of the lightare harmonic as e^(l({right arrow over (k)}·{right arrow over (x)}−ωt))then we can write the wavevector as $\begin{matrix}{{k = {\beta + {i\frac{\alpha}{2}}}},} & (3.)\end{matrix}$

[0090] where $\begin{matrix}{{\left. \begin{matrix}\beta \\\frac{\alpha}{2}\end{matrix} \right\} = {\sqrt{\mu \quad ɛ}{\frac{\omega}{c}\left\lbrack \frac{\sqrt{1 + \left( \frac{4\quad \pi \quad \sigma}{\omega \quad ɛ} \right)^{2}} \pm 1}{2} \right\rbrack}^{1/2}}},} & (4.)\end{matrix}$

[0091] where μ is the magnetic permeability, ε is the dielectricconstant, σ is the conductivity of the material, c is the speed oflight, and ω=E/h is the circular frequency of the light.

[0092] Inserting Eq. (4.) into Eq. (3.), and using thee^(l({right arrow over (k)}·{right arrow over (x)}−ωt)) dependency, wesee that the amplitude of the light incident in the z direction willdrop off exponentially as e^(−az/2), and hence the intensity will go ase^(−az), verifying that α is indeed the attenuation coefficientmentioned earlier. Hence, a change in the conductivity, σ, in Eq. (4.)will result in a corresponding change in the attenuation coefficient, σ.

[0093] Although the above classical treatment is not sufficient todescribe the details of the interactions of photons with the conductionband electrons, the qualitative property of the conductivity affectingthe absorption coefficient still holds true. For a more completedescription, one must treat the system quantum mechanically. The nextsection deals with the quantum mechanical interaction of light with asolid.

[0094] Absorption Via Atomic/interband Photoeffect

[0095] In this case, an electron absorbs an incident photon and ispromoted to an excited state. If the energy of the light is insufficientto liberate it from the material completely (photoelectric knockout),then the electron must be promoted into another quantized state in thematerial. If such a state does not exist, the incident photon is notabsorbed because energy cannot be conserved. Furthermore, if the statedoes exist but is already occupied by another electron (ignoring spin),the transition is also forbidden by the Pauli principle. If thetransition is allowed, the probability that such an interband transitionwill occur can be written

P _(if)(E ₇)∝T _(if) g _(f)(E _(f))g _(i)(E _(i)), with E _(f) =E _(i)+E _(y),  (5.)

[0096] where T_(if) is the transition matrix element, g_(i)(E_(i)) isthe density of states initially occupied by electrons, and g_(f)(E_(f))is the density of unoccupied final states into which the electron may bepromoted. The attenuation coefficient is proportional to thisprobability, P_(if). Hence, if one can change either g_(i) or g_(f) thenone can effectively make the material “transparent” or “opaque”.

[0097] To illustrate how the absorption can be controlled in a shutterwe now look to specific examples.

[0098] We will consider a Metal-Oxide-Semiconductor device (“MOS”) as anexample, but the discussion could also be applied to other structuressuch as p-n junctions, and even insulators. The region of interest willbe in the semiconductor, near the interface with the oxide. Thesemiconductor has a band gap which we will choose to be 1 eV. In theintrinsic case, light with an energy less than 1 eV incident on thesemiconductor is not able to promote electrons from the valence band tothe conduction band. Hence, interband transitions will not contribute tothe attenuation coefficient. The “free” electrons in the conduction bandsolely interact with the incident light. With this, if we consider thecase where we dope the semiconductor as n-type (i.e. adding more freeelectrons to the conduction band), more light will be absorbed as weincrease the dopant concentration (because there are more electronsinteracting). For light energies less than the band gap, is we willconsider the material to then be “opaque” to the light, as the electronsin the conduction band absorb a significant amount of the incidentintensity.

[0099] Next, if we apply a voltage to the MOS structure, we create aregion near the interface in which the number of conduction bandelectrons is reduced compared to the non-biased case. Now we have asituation where the amount of light absorbed is less, because we have ineffect changed the conductivity of the semiconductor in this depletionregion. This situation is “transparent” relative to the aforementioned“opaque” setup. The actual materials used and the technique for creatingthe depletion region should be chosen in such a way to maximize thecontrast, C, while keeping the actual transmitted intensity,I^(transparent), as large as possible (so that the process takes aslittle time as possible.)

[0100] Another example would be to choose incident light with an energyjust larger than the band gap energy. Then, interband transitions arelikely to dominate the absorption. In the same n-type doped MOSstructure as above, the density of unoccupied states in the conductionband, g_(f), into which a valence band electron can be promoted isreduced near the bottom of the conduction band. This is due to thepresence of a large concentration of electrons from the dopant atoms.Now, consider the situation in which we apply a voltage across theinterface. This creates a depletion region in which there are fewerelectrons present in the conduction band, and hence more unoccupiedstates. Comparing the biased and unbiased situations, one can see thatthe latter should be more “opaque” than the former, because more valenceband electrons can be promoted into the newly vacated conduction bandstates. Once again, materials and voltages, etc. . . can be chosen tomaximize both contrast and “transparent” intensity. Also, if we had usedp-type doping rather than n-type, a corresponding change in g_(i) wouldhave appeared. Depleting the region of holes would have the same effectof toggling the state of the shutter. One should note that in thepreviously stated examples, the attenuation coefficient is onlyappreciably changed for a specific range of light energies, determinedby properties such as but not limited to the choice of materials in theMOS structure, the bias supplied, and the dopant density. It should alsobe noted that this transition-blocking effect can work for photonenergies corresponding to any transition within the material. Forexample, changing the density of unoccupied states in the conductionband, g_(f), can affect the absorption of light (x-rays) on inner shellelectrons in a material. Higher energies of light are desirable inlithography because the effects of diffraction are reduced as the lightenergy is increased.

[0101] Next, for the preferred embodiment array of selective amplifiersto work, it is necessary that the various selective amplifiers can bemade either “amplifying” or “non-amplifying” to the incident light. Fora mask, both terms “amplifying” and “non-amplifying” describe the ratioof the intensity of incident light to the intensity of output light. An“amplifying” state is defined relative to a “non-amplifying” state inthat the amount of light at the output is much greater. Using this, ifwe compare the output intensities through an “amplifying” material and a“non-amplifying” material, we get a measure of the contrast in lightimpinging on the resist, C, as $\begin{matrix}{{C = {\frac{I_{amplifying}}{I_{{non}\text{-}{amplifying}}} = \frac{I_{amplifying}}{I_{o}}}},} & (6.)\end{matrix}$

[0102] where I_(non-amplifying) is the incident intensity I₀, andI_(amplifying) is the output intensity. The contrast is typically anincreasing function of the thickness of the selective amplifier.

[0103] If this contrast is a large number, the resist will only beactively exposed when the selective amplifier is in the “amplifying”state. Thus, if we can control the amount of amplification in a materialsuch that C is large, then the system is a useful candidate for use in aprogrammable mask.

[0104] The amplification occurs by a process known as stimulatedemission. If an electron exists in a state that is an energy ΔE aboveanother state, then when the electron drops (makes a transition) fromthe higher state to the lower state it will emit a photon with energyΔE. A photon with energy ΔE that passes near the electron in the excitedstate can cause the electron to drop to the lower state and emit aphoton with the same energy, phase, and direction as the first photon.This is the process of stimulated emission. Stimulated emission is awell-known process and is the basis of the laser. In order forstimulated emission to occur, several conditions must be met. Onecondition is that there must be a population inversion. Ordinarily,electrons are in the lowest state available to them. When there are moreelectrons in an excited state than in the lower state then a populationinversion exists. Another condition for stimulated emission is thatthere must be initial photons of the proper energy to cause theelectrons to drop from the excited state.

[0105] In the preferred embodiment of the array of selective amplifiers,biasing the p-n junctions causes population inversions and the incidentlight provides the initial photons necessary for stimulated emission.The light that is shined on the biased p-n junctions is thereforeamplified; the biased situation is the aforementioned “amplifying”state. The light that is incident on the unbiased p-n junctions istransmitted but not amplified. This allows the incident light to beselectively amplified by controlling which p-n junctions are biased. Aslong as there is appreciable amplification, and hence appreciablecontrast, selective amplifiers can be useful in a lithography system.

[0106] Although the preferred embodiment describes a complex device thatcombines various components, each component in itself represents eithera new technology or a great improvement upon existing technology. Forexample, an array of selective amplifiers or an array of shutters couldbe used as a stand-alone programmable structure, either with or withouta diffraction limiter. Additionally, either type of array or adiffraction limiter could be implemented as part of any programmablelithography scheme.

[0107] Therefore, while the invention has been described in connectionwith what is presently considered to be the most practical and preferredembodiment, it is to be understood that the invention is not to belimited to the disclosed embodiment, but on the contrary, is intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims.

We claim:
 1. A method of exposing a wafer comprising: placing at leastone two-dimensional array of structures between a wafer and a source ofelectromagnetic energy, said structures each comprising an active regionsupporting an electron distribution that can be changed to affect themodulation of electromagnetic energy from said source; and controllingthe structures to selectively modulate, in accordance with aprogrammable pattern, electromagnetic energy impinging on the wafer. 2.A method as in claim 1 wherein at least some of the active regionscomprise a material having a band gap.
 3. A method as in claim 1 whereinat least some of the active regions comprise semiconductor material. 4.A method as in claim 1 wherein the controlling step includes applying atleast one of (a) a voltage, and (b) a current, to said structures.
 5. Amethod as in claim 1 wherein the structures each comprise at least oneof a PN junction semiconductor structure and ametal-insulating-semiconductor structure.
 6. A method as in claim 1wherein the controlling step (b) comprises: (b1) controlling saidstructures to selectively modulate the electromagnetic energy impingingon the wafer in accordance with a first pattern; and (b2) controllingsaid structures to selectively modulate the electromagnetic energyimpinging on the wafer in accordance with a second pattern differentfrom the first pattern.
 7. A method as in claim 6 wherein steps (b1) and(b2) result in exposing, in an overlayed manner, the same part of thewafer.
 8. A method as in claim 6 wherein steps (b1) and (b2) result inexposing different, adjacent regions of the wafer to provide an exposurepattern that is larger than the modulated electromagnetic energy patternimpinging on the wafer at any one time.
 9. A method as in claim 6further including moving the wafer between step (b1) and step (b2). 10.A method as in claim 1 wherein each of said structures comprises anelectromagnetic energy shutter.
 11. A method as in 10 wherein each ofsaid structures further comprises an electromagnetic energy amplifier.12. A method as in claim 1 wherein each of said structures comprises anelectromagnetic energy amplifier.
 13. A method as in claim 1 furtherincluding: aligning at least one of structures with a wafer feature;determining the position of said array relative to said wafer; andprogramming said array to offset an exposure pattern within said arraysuch that said exposure pattern is located correctly on said wafer. 14.A method as in claim 1 further including the step of disposing adiffraction limiter between said array and said wafer.
 15. A system ofexposing a wafer comprising: at least one two-dimensional array ofstructures disposed between a wafer and a source of electromagneticenergy, said structures each comprising an active region supporting anelectron distribution that can be changed to affect the modulation ofelectromagnetic energy from said source; and a controller that controlsthe structures to selectively modulate, in accordance with aprogrammable pattern, electromagnetic energy impinging on the wafer. 16.A system as in claim 15 wherein at least some of the active regionscomprise a material having a band gap.
 17. A system as in claim 15wherein at least some of the active regions comprise semiconductormaterial.
 18. A system as in claim 15 wherein the controller includesdriver circuitry that applies at least one of (a) a voltage, and (b) acurrent, to said structures.
 19. A system as in claim 15 wherein thestructures each comprise at least one of a PN junction semiconductorstructure and a metal-insulating-semiconductor structure.
 20. A systemas in claim 15 wherein the controller controls said structures toselectively modulate the electromagnetic energy impinging on the waferalternatively in accordance with at least (a) a first pattern, and (b) asecond pattern different from the first pattern.
 21. A system as inclaim 20 wherein controller controls the array to overlay said first andsecond patterns onto the same part of the wafer.
 22. A system as inclaim 20 wherein the controller controls the array to expose different,adjacent regions of the wafer to provide an exposure pattern that islarger than the modulated electromagnetic energy pattern impinging onthe wafer at any one time.
 23. A system as in claim 20 further includingmeans for moving the wafer between the first pattern exposure and thesecond pattern exposure.
 24. A system as in claim 15 wherein each ofsaid structures comprises an electromagnetic energy shutter.
 25. Asystem as in 24 wherein each of said structures further comprises anelectromagnetic energy amplifier.
 26. A system as in claim 15 whereineach of said structures comprises an electromagnetic energy amplifier.27. A system as in claim 15 further including: means mechanicallycoupled to at least one of the array and the wafer, for aligning atleast one of structures with a wafer feature; and means for determiningthe position of said array relative to said wafer, and wherein thecontroller programs said array to offset an exposure pattern within saidarray such that said exposure pattern is located correctly on saidwafer.
 28. A system as in claim 15 further including a diffractionlimiter disposed between said array and said wafer.
 29. Apparatus forexposing a wafer using an illumination source, said apparatuscomprising: means disposed between said wafer and said illuminationsource for modulating electromagnetic energy passing therethrough to thewafer, said means for modulating comprising at least one two-dimensionalarray of plural means for supporting an electron distribution that canbe changed to affect the modulation of electromagnetic energy from saidillumination source; and means, coupled to the means for supporting, forcontrolling the means for supporting to selectively modulate, inaccordance with a programmable pattern, electromagnetic energy impingingon the wafer.
 30. Apparatus as in claim 20 wherein at least some of themeans for supporting at least in part comprise a material having a bandgap.
 31. Apparatus as in claim 20 wherein at least some of the means forsupporting at least in part comprise semiconductor material. 32.Apparatus as in claim 20 wherein the means for controlling includesmeans for applying at least one of (a) a voltage, and (b) a current, tosaid means for supporting.
 33. Apparatus as in claim 20 wherein themeans for supporting each comprise at least one of a PN junctionsemiconductor structure and a metal-insulating-semiconductor structure.34. Apparatus as in claim 20 wherein the means for controllingcomprises: means for controlling said means for supporting toselectively modulate the electromagnetic energy impinging on the waferin accordance with a first pattern; and means for controlling said meansfor supporting to selectively modulate the electromagnetic energyimpinging on the wafer in accordance with a second pattern differentfrom the first pattern.
 35. Apparatus as in claim 34 wherein said meansfor controlling causes the same part of the wafer to be exposed in anoverlayed manner with the first pattern and the second pattern. 36.Apparatus as in claim 34 wherein said means for controlling causedifferent, adjacent regions of the wafer to be exposed with the firstand second patterns, to provide an overall exposure pattern that islarger than the modulated electromagnetic energy pattern impinging onthe wafer at any one time.
 37. Apparatus as in claim 34 furtherincluding means for moving the wafer between exposure with the firstpattern and exposure with the second pattern.
 38. Apparatus as in claim20 wherein each of said means for supporting comprises anelectromagnetic energy shutter.
 39. Apparatus as in 38 wherein each ofsaid means for supporting further comprises an electromagnetic energyamplifier.
 40. Apparatus as in claim 20 wherein each of said means forsupporting comprises an electromagnetic energy amplifier.
 41. Apparatusas in claim 20 further including: means for aligning at least one ofsaid means for supporting with a wafer feature; means for determiningthe position of said array relative to said wafer; and means forprogramming said array to offset an exposure pattern within said arraysuch that said exposure pattern is located correctly on said wafer. 42.Apparatus as in claim 20 further including a diffraction limiterdisposed between said array and said wafer.
 43. A system for exposing awafer comprising: a source of electromagnetic energy; a collimating lensoptically coupled to the electromagnetic energy source; a wafer stage; atwo-dimensional array of structures disposed between the wafer stage andthe collimating lens, each said structures in the array comprising anactive region supporting an electron distribution that can be changed toaffect the modulation of electromagnetic energy from said source; and anelectrical controller coupled to the two-dimensional array, thecontroller electrically controlling the semiconductor structures toselectively modulate, in accordance with a changeable pattern,electromagnetic energy from the source that is directed toward the waferstage.
 44. A method of making integrated circuits comprising: providinga wafer having a surface covered with photoresist; placing the wafer ona movable wafer stage; directing electromagnetic energy toward atwo-dimensional array of semiconductor structures disposed between asource of said electromagnetic energy and said wafer stage; electricallycontrolling the electron distribution within the structures to define adesired microfabrication exposure pattern that modulates electromagneticenergy from said source that impinges on the wafer in accordance with apattern, thereby exposing the photoresist with said pattern; etching thewafer to selectively remove portions of said photoresist based on saiddesired microfabrication exposure pattern; and treating said etchedwafer to construct a semiconductor structure layer on said wafer.
 45. Asystem for making integrated circuits from wafers, the systemcomprising: a source of electromagnetic energy; means for providing awafer having a surface covered with photoresist; means for placing thewafer on a movable wafer stage; means for directing electromagneticenergy toward a two-dimensional array of semiconductor structuresdisposed between the source of said electromagnetic energy and saidwafer stage; means for electrically controlling the electrondistribution within the two-dimensional array of semiconductorstructures to selectively modulate the electromagnetic energy impingingon the wafer in accordance with a desired microfabrication exposurepattern, thereby exposing the photoresist with said pattern; means foretching the wafer to selectively remove portions of said photoresistbased on said desired microfabrication exposure pattern; and means fortreating said etched wafer to construct a semiconductor structure layeron said wafer.
 46. A system as in claim 45 further comprising adiffraction limiter disposed between the wafer stage and thetwo-dimensional array.
 47. In a semiconductor chip fabrication line, awafer exposing unit comprising: a movable wafer stage for supporting andpositioning a wafer having a surface covered with photoresist; acontrollable source of electromagnetic energy; a two-dimensional arrayof semiconductor structures disposed between said source of saidelectromagnetic energy and said wafer stage, the structures within thearray each comprising an active region supporting an electrondistribution that can be changed to affect the modulation ofelectromagnetic energy from said source; a pattern generator thatdefines a microfabrication pattern; and an electrical controller coupledto the two-dimensional array and the pattern generator, the electricalcontroller electrically changing the electron distributions within eachof the semiconductor structure active regions to selectively modulatethe electromagnetic energy impinging on the wafer in accordance withsaid microfabrication exposure pattern, thereby exposing the photoresistwith said pattern.
 48. A system as in claim 47 further comprising adiffraction limiter disposed between the wafer stage and thetwo-dimensional array.
 49. A programmable structure for use inmicrofabrication lithography of a wafer, the programmable structurecomprising: a two-dimensional array of semiconductor structures eachcomprising an active region supporting an electron distribution that canbe changed to affect the modulation of electromagnetic energy from saidsource; and electronics coupled to the semiconductor structures, theelectronics electrically controlling the semiconductor structures toselectively modulate electromagnetic energy impinging on the wafer inaccordance with a microfabrication pattern.
 50. A system as in claim 49wherein the semiconductor structures comprise semiconductor shutters.51. A system as in claim 49 wherein the semiconductor structurescomprise MOS structures.
 52. A system as in claim 49 wherein thesemiconductor structures comprise PN junctions.
 53. A system as in claim52 wherein the electronics includes means for changing the bias acrosseach of the PN junctions.
 54. A system as in claim 49 wherein thesemiconductor structures each include an active semiconductor regionthat can be electrically switched between a state of relatively highoptical transmissivity and a state of relatively low opticaltransmissivity.
 55. A system as in claim 49 wherein the semiconductorstructures each comprise an active semiconductor region that isselectively, electrically controllable to switch between an amplifyingstate and a non-amplifying state.
 56. A system as in claim 49 whereinthe semiconductor structures comprise optical amplifiers.
 57. A methodof making a programmable mask for use in microfabrication lithography,the method comprising: incorporating a plurality of semiconductorstructures into a two-dimensional array, said structures each comprisingan active region supporting an electron distribution that can be changedto affect the modulation of electromagnetic energy; incorporating intosaid array, electrical circuitry coupled to the semiconductor structurethat electrically controls the semiconductor structures to operate indifferent electromagnetic modulating states; and testing said array byoperating said electrical circuitry to determine whether the array iscapable of selectively modulating electromagnetic energy in accordancewith a two-dimensional test pattern.
 58. A programmable electromagneticenergy modulating structure comprising: a two-dimensional array ofsolid-stage shutters each comprising regions of permanently opaqueregions and active regions; and control circuitry disposed within thearray, the control circuitry selectively controlling each of the activeregions to toggle between an opaque stage and a transparent state.
 59. Aprogrammable electromagnetic energy modulating structure comprising: atwo-dimensional array of solid-state selective amplifiers eachcomprising regions of permanently opaque material and active regions;and control circuitry disposed within the array, the control circuitryselectively controlling each of the active regions to toggle between anamplifying state and a non-amplifying state.
 60. A diffraction limiterfor use in microfabrication, said diffraction limiter comprising atwo-dimensional array of transparent regions and opaque regions, saidtransparent regions having locations individually corresponding to thelocations of the active regions of a programmable mask.
 61. A method ofexposing a wafer comprising: placing a structure between a wafer and asource of electromagnetic energy; illuminating said structure withelectromagnetic energy from said source; amplifying, with saidstructure, a portion of the incident electromagnetic energycorresponding to a pattern; and outputting, from said structure to saidwafer, said amplified electromagnetic energy corresponding to saidpattern.
 62. A method as in claim 61 wherein said pattern issubstantially permanently defined.
 63. A method as in claim 61 furtherincluding the step of programming the pattern into said structure.
 64. Asystem of exposing a wafer comprising: means for placing a structurebetween a wafer and a source of electromagnetic energy; means forilluminating said structure with electromagnetic energy from saidsource; means for amplifying, with said structure, a portion of theincident electromagnetic energy corresponding to a pattern; and meansfor outputting, from said structure to said wafer, said amplifiedelectromagnetic energy corresponding to said pattern.
 65. A system as inclaim 64 wherein said pattern is substantially permanently defined. 66.A system as in claim 64 further including the step of programming thepattern into said structure.
 67. A method of exposing a wafercomprising: placing a structure between a wafer and a source ofelectromagnetic energy, said structure comprising a first region inwhich the electron distribution has been altered relative to a secondregion; illuminating said structure with electromagnetic energy fromsaid source; masking, with said structure, a portion of the incidentelectromagnetic energy corresponding to a pattern; and outputting, fromsaid structure to said wafer, said masked electromagnetic energycorresponding to said pattern.
 68. A method as in claim 67 wherein saidfirst region has a different doping level than the second region.
 69. Amethod as in claim 67 wherein said structure comprises a material with aband gap.
 70. A method as in claim 67 wherein said structure comprises asemiconductor material.
 71. A method as in claim 67 wherein saidelectromagnetic transmissivity of said first region and said secondregion are substantially permanently defined.
 72. In a step and repeatlithography system, a method for electronically aligning an exposurepattern with a wafer having at least one feature, during amicrofabrication process, the method comprising: providing aprogrammable two-dimensional array defining plural picture elements;aligning at least one of said picture elements with said wafer feature;measure the position of said array relative to said wafer; andprogramming said array to offset an exposure pattern within said arraysuch that said exposure pattern is located correctly on said wafer. 73.A programmable structure for use in microfabrication lithography of awafer, the programmable structure comprising: a two-dimensional array oflight sources; and electronics coupled to the light sources, theelectronics electrically controlling the light sources to selectivelyemit electromagnetic energy impinging on the wafer in accordance with amicrofabrication pattern.
 74. A structure as in claim 73 wherein thelight sources comprise semiconductor lasers.